The indoor environment is a significant concern in designing and building various structures. Human and occupant comfort are largely affected by airflow, thermal comfort and relevant temperature. Airflow is generally the measurable movement of air across a surface. Relevant temperature is the degree of thermal discomfort measured by airflow and temperature. Airflow that improves an employee health and productivity can have a large return on investment. High-volume, low-speed ceiling and vertical fans can provide significant energy savings and improve occupant comfort in large commercial, industrial, agricultural and institutional structures. High-volume low-speed (HVLS) fans are the newest ventilation option available today. These large fans, which range in size from 8 to 24 feet, provide energy-efficient air movement throughout a large volume building at a fraction of the energy cost of high-speed fans.
The main advantage of an HVLS fan is its limited energy consumption. One 20-foot fan typically moves approximately 125,000 cubic feet per minute (cfm) of air. It takes six to seven standard fans to provide similar volume of air movement. An eight-foot fan can move approximately 42,000 cfm of air. Most HVLS fans employ a 1 to 2 HP motor, moving the same volume of air (for approximately one-third of the energy cost) of six high-speed fans.
HVLS fans move large columns of air at a slow velocity, about 3 mph (260 fpm). Air movement of as little as 2 mph (180 fpm) has been shown to provide a cooling effect on the human body according to the Manual of Naval Preventive Medicine. In fact, airflow at 2 mph will give a cooling effect of approximately 5° F. (the air feels 5° F. cooler) and an airflow of 4 mph will provide a cooling effect of approximately 10° F.; that is if the actual temperature was 75° F. with an airflow of 4 mph, the relative temperature would be 65°. The cooling effect is described as the retentive temperature. Moreover, it has been shown that turbulent airflow provides a more-effective cooling sensation than uniform airflow by David W. Kammel, et al., “Design of High Volume Low Speed Fan Supplemental Cooling System in Free Stall Barns.”
A study done by the University of Wisconsin shows that HVLS systems provide more widespread air movement throughout the building or space to be cooled. One disadvantage of traditional HVLS fans is that they have an area of “dead” air (air that has minimal air movement) in close proximity to the centerline of the fan.
Although high-speed fans provide more velocity, each unit impacts only a small, focused area. High-speed fans are good for managing extreme heat, although they can cause a dramatic increase in energy consumption in the hot, summer months. High-speed fans produce higher velocities in the area directly surrounding each fan, leaving large areas of dead air outside the diameter of the fan blades.
HVLS systems are sometimes used year-round. In summer, HVLS fans provide essential cooling; in winter, the fans move drier air from ceiling to floor level and may result in a more comfortable environment. HVLS fans are virtually noiseless. HVLS fans provide more comfort to individuals positioned in proximity to the fan, because the airflow causes a lower relevant temperature—that is, the air temperature feels cooler because of the movement of the air. The optimal airflow velocity for HVLS fans is typically between 2 to 4 miles per hour for most operations. Spacing the fans too far apart will significantly diminish the system's benefits.
HVLS fans cost approximately $4,200-$5,000 each, including installation. While this is a large upfront investment, facility must use six to seven high-speed fans at $200-$300 each to move the same volume of air as with one HVLS fan. Energy savings realized through the use of HVLS fans over a high-speed fan system should make up the cost difference within two to three years. Manufacturers claim that HVLS fans typically do not require replacement for at least 10 years. Because high-speed fans operate a higher RPM, the motors typically need to be replaced more frequently than with HVLS fans.
The components of a typical fan include:                An electromagnetic motor;        Blades also known as paddles or wings (usually made from wood, plywood, iron, aluminum or plastic);        Metal arms, called blade mounts (alternately blade brackets, blade arms, blade holders, or flanges), which hold the blades and connect them to the motor;        A mechanism for mounting the fan to the ceiling.        
There are axial flow fan blades available in the prior art that address the issue of increasing the efficiency of a fan. For example, U.S. Pat. Nos. 4,089,618, 5,603,607 and 5,275,535 all pertain to fan blades in which the trailing edges contain notches or a saw-tooth shape. Additionally, in U.S. Pat. No. 5,275,535, both the leading and the trailing edges are notched. Moreover, U.S. Pat. Nos. 5,326,225 and 5,624,234 disclose fan blade platform shapes that are curved forward and backward. Despite the fact that the referred patents may present a reduction on the noise level and an increase on the efficiency, the improvement obtained is quite modest. Consequently, the applicability of these patents is limited in actual practice. Another prior art technology, as depicted in U.S. Pat. No. 8,535,008, utilizes a leading edge which includes a series of spaced “tubercles” formed along the leading edge of the rotor blade.
None of the prior art shows a stepped blade configuration along the leading edge of a fan blade. There is a need for a stepped leading edge fan blade design that creates turbulent airflow and delivers an increased velocity over a greater area.